Calling key testing apparatus



Dec. 22;"1942. J. T. NElswlNTER 2,306,220

CALLING KEY TESTING APPARATUS Filed Aug. 1s, 1941 ATTORNEY Patented @ed22, 1942 iran stars f YOFFICE CALLING KEY TESTING APPARATUS ApplicationAugust 13, 1941, Serial No. 406,582

3 Claims.

This invention relates in general to signaling apparatus, and moreparticularly to teletypewriter apparatus. relates to arrangements forobserving the operation and performance of calling keys or switches andthe like.

In existing signaling systems a key which is frequently called a Gillselector key is used for calling any one of a plurality of parties whichmay be connected to a line. This key comprises a rotatable wheel whichincludes a plurality of groups of notches each of which is uniformly cutalong the periphery of the wheel. One of the contacts of a switch restson an arm which rides along the periphery of the key wheel while thelatter rotates and as it engages one of the notches it may be used tointerrupt a signaling current. Thus the signaling current will beinterrupted a predetermined number of times corresponding to the notchesin the key wheel during its rotation through one complete revolution andhence a corresponding number of pulses will be generated. These pulsesmay :be transmitted over the circuit and impressed upon a plurality ofselectors, but only that selector which is designed to respond to thegroups of pulses of a particular key will be actuated by those pulsesfor apprising, for example, the attendant at the station ywhere theselector is located that he is being called on the circuit.

At present difficulties are experienced with keys of pulses set up bythe key. The usual result of this condition is that considerable time isspent in readjusting or replacing keys and selectors until the troubleis ultimately cleared. This cut Still more particularly this invention'and try practice is, of course, time consuming and.

ofttimes involves the unnecessary replacement of of the type abovereferred to so that their performance may be studied and they may beadjusted for proper operation. The apparatus used will include ateletypewriter which may be located in any one of the ofces on thecircuit or at the central oiilce. employed will yield a ready check onthe operation and the mechanical adjustment of the key. The arrangementsto be described may also be used for observing and checking theoperation of the key The method and apparatus to be "i" predeterminedgroups of pulses.

service on the circuit. The method and apparatus to be described mayindicate troubles due to the customers operation of the signal key thatmay not be evident during tests performed by a maintenance man.

This invention will be better understood from the detailed descriptionhereinafter following, when read in connection with the accompanyingdrawing, in which Figure 1 shows one form of circuit arrangement whichmay be used for observing the performance of a calling key of the typealready referred to; Fig. 2 shows an arrangement to explain the generalprinciples of the calling key and its associated switch contacts; Fig.3a illustrates an analysis of one of the pulses of the calling key; andFig. 3b shows a chart of teletypewriter code characters that may beprinted to indioate the satisfactory or unsatisfactory operation of thecalling key.

Referring to Fig. 1 of the drawing, there is shown a loop circuit inwhich are located three customers stations designated Nos l, 2 and 3.The loop circuit may terminate in a central oice CO. Each station mayinclude a pair of calling keys, a selector and a teletypewriter. Thecalling keys at station No. l, for example, are designated K12 and K13,the key K12 being employed to call the attendant at station No. 2 andkey K13 the attendant at station No. 3. Likewise the keys K21 and Kza atstation No. 2 may be employed to signal to stations Nos. l and 3, andkeys K11 and Kaz of station No. 3 may signal stations Nos. I and 2,respectively. The selectors S1, S2 and S3 at the three respectivestations will each respond to but one of the codes that may betransmitted over the circuit. The selector S1, for example, will respondto the codes prepared by keys Kzi and Kn at stations Nos. 2 and 3,respectively, the latter keys both preparing the same Likewise theselector Sz at station No. 2 will respond to the code prepared by keysK12 and KS2 at stations I and 3, respectively, which also prepare thesame groups of pulses and, finally, the selector S3 may be operated bythe groups of pulses prepared by keys K13 and Kga at stations Nos l and2, respectively. A typical group of pulses prepared by one of the keysmay, for example, be 6, 5, 4, 2, 1, 1-1, where the initial group of six-pulses is used to clear the various selectors and the nal pulse afterthe dash releases the particular selector stepped and operated by thecode received. It will be apparent that upon the operation of one of theselectors such as S1, a signal device may be operated or its even whenit is used by the customer during actual 55 associated teletypewriter T1may be operatively connected to the circuit for communication with thecalling station or, if desired, both of these functions may be performedat the same time.

The central oiice CO may include a teletypewriter To for observing theperformance of any of the Various keys at the outlying stations.Although the circuit shown in Fig. 1 represents a direct current loopcircuit, a similar arrangement may be employed for signaling betweenoices employing voice frequencies or higher frequencies, and repeaters(not shown) may be added to the circuit wherever required. A generaldescription of teletypewriters that may be used in the circuit of Fig. 1is given in Pender- McIlwains Electrical Engineers Handbook onCommunication-Electronics, third edition, pages 11-23 and 1l-24.

The general outline of the rotatable wheel of the calling key and thecontacts which are controlled thereby are shown in Fig. 2. Here thecircular rotatable member W includes a plurality of peripheral notchesaccording to the code 6, 5, 4, 2, 1, 1l. Each group of notches is spacedfrom each succeeding group and the spacing is uniform between allgroups, except that the spacing between the last notch N and thepreceding notch is considerably greater than the spacing between thevarious preceding groups of notches. The switchcontacts are designatedK1 and K2. The contact K1 is of a spring type and may be made of amaterial such as phosphor bronze. The contact K1 bears against a narrowbar Y which may be inserted into each of the various notches as thewheel W of the key rotates in the direction indicated by the arrow. Thepressure applied by the spring contact K1 against bar Y acts to hold thearm Yin engagement with the outer surface of the wheel W during itsrotation.

As the wheel W rotates in a clockwise direction, the arm Y in followingthe contour of the wheel W will move downward into 'the successivenotches and hence open the circuit of'the contacts K1 and K2. Thevarious interruptions or opens introduced by the notches are allintended to be of the same duration as, for example, 183 milliseconds.The spacings between the successive interruptions of any two pulses ofany group 'of pulses are also uniform and may be, for'example, 133 ms.Ofttimes failure in operating a selector is due to the fact that theinterruptions or opens are substantially different from 183 ms. althoughsmall deviations from this standard Value will ordinarily not interferewith the satisfactory operation of the apparatus as will be describedhereinafter.

Fig. 3a shows a standard 183 ms. interruption or open produced by acalling key such as key K12 of Fig. 1, and directly below it Fig. 3bshows the receiving time chart of a 60 speed teletypewriter with thesuperimposed code characters that may be printed on a teletypewritersuch as To, located at the central oflice CO of Fig. 1. It will beunderstood that in 60 speed teletypewriter operation there are astarting pulse of 22 ms. and ve code signals each also of 22 ms., and anal or stop" pulse of 11 ms. for a receiving apparatus. The total timefor one of these teletypewriter characters will therefore be 143 ms.Inasmuch as the 183 ms. interruption or open of the calling key islongerthan the time for one 60 speed teletypewriter character, theteletypewriter cam (not shown), which will be released once at thebeginning of the open and a second time at the end of the stop pulse(after 143 ms.) will therefore rotate through two complete revolutionsduring the production of but one interruption or open of the callingkey.

If the calling key interruption is of the standard value of 183 ms.,`the teletypewriter To, for example, will print the letter V for eachsuch interruption. Hence the teletypewriter will print a series of Vscorresponding to the number of notches of the wheel W of the callingkey. In actual practice there may be irregularities in the constructionand operation of the key so that 1 the opens of the key will be longerthan 183 ms.

Such longer pulses may be long enough to print the Ms of theteletypewriter code. Thus certain keys may print Vs and others Ms and ifstill longer interruptions are produced, Os, Ts and even blanks may beproduced. On the other hand, if the open is shorter than 183 ms., theletters combination may be received on the teletypewriter. On someteletypewriters nothing may be printed for either the blank or theletters combination, but on other machines which are arranged to printon either blank or letters combination, the 183 ms. interrup tion willprint characters such as arrows to desig' nate these combinations.

The length of any interruption or open in general is dependent upon theadjustment of its sending contacts K1 and K2 and also upon the speedwith which the wheel W of the key rotates. It will be understood, ofcourse, that the wheel when released is rotated clockwise under controlof its own governor from its initial position shown in Fig. 2 andthereby produces the various groups of pulses characteristic of the keyoperated. When the speed of the wheel W of the key is relatively slow,the interruptions will be longer than 183 ms., and on the other hand,when the speed is greater than normal, the interruptions will be lessthan 183 ms. The time for one revof lution of the wheel may be checkedat the central oice CO by measuring the time interval between the rstpulse which is produced when the arm Y engages the notch N1 and the lastpulse produced when the arm Y engages the notch N1. This time intervalcan be measured, for example, on a stop watch. The opens may be detectedby a sounder or a teletypewriter or other equivaient apparatus. The lastopen is distinguished by its appearance after the long pause thatseparates the nal pulse from the previous pulses. Although the time someasured indicates merely an interval somewhat less than that of onecomplete revolution (due to the omission of the brief interval betweenthe pulses N1 and N'i), this discrepancy represents but a very smallfraction of a second and may in practice either be ignoredor'compensated in the calculations.

The time of operation of the key should be adjusted to be somewhere, forexample, between 14 and 16 seconds. The period of a revolution shouldnot be less than 14 seconds because in that case the opens and closes ofthe key may be so short as to fail to operate the receiving selector. Ifthe period of operation is more than 16 seconds, the signaling time maybe unnecessarily prolonged. Of these two possibilities, however, it ispreferable to favor the positive operation of the selector by confiningthe operating time of the key closer to the 16 than to the 14 secondinterval.

After the key has been adjusted so that its rotating time will be withinpredetermined limits, then the characters that the key causes theteletypewriter to print are indicati-ve of the adjustment of the sendingcontacts K1 and K2 of the key. If the contacts remain open too long, Osand Ts will be printed by the teletypewriter. On the other hand, if thecontacts do not remain open long enough, the letters or blankcombinations Will be received by the teletypewriter. The danger inhaving the contacts not remain open long enough is that the receivingselector may fail to operate on the short opens while if the contactsremain open too long the close between two interruptions will not belong enough, i. e., the close will be less than 133 ms. and the selectormay then fail to respond properly.

Thus after the operating time of the key has been checked and adjustedto be Within prescribed limits, the key may be, operated and thecharacters printed on the teletypewriter observed. 'Ihe printing of Vsand Ms will indicate satisfactory operation of the key and its contactswhile the reception of other teletype- Writer characters Will generallyindicate unsatisfactory operation. Os and Ts indicate interruptionsWhich are too long and letters and blanks indicate interruptions Whichare too short. The number of characters printed ought to correspond tothe number of notches or digits in the code of the key being tested.

It will be understood that the various constants recited hereinabove aregiven merely for the purpose of illustration and are not to be construedas limitations upon the inventions. Other constants of Widely diierentcharacter may, of course, be employed in practice Within the scope ofthis invention.

While this invention has been shown and described in certain particulararrangements merely for the purpose of illustration, it will beunderstood that the general principles of this invention may be appliedto other and widely varied inventions without departing from the spiritof the invention and the scope of the appended claims.

What is claimed is:

1. The method of determining the length of each interruption produced bya pulse producing key having a plurality of notches to provide aplurality of pulses with each operation of the key, with apparatusincluding a teletypewriter, which consists in operating theteletypewriter at vthe beginning of each interruption and then printinga teletypewriter character at the end of each interruption, the printedcharacters corresponding to the lengths of the interruptions.

2. In apparatus for testing a multi-notched key which produces aplurality of current interruptions of substantially uniform lengths witheach operation of said key, the apparatus including a teletypewriterconnected to the circuit of the key, the method of determining theduration of each interruption produced by said key which consists inoperating the teletype- Writer at the beginning of each interruption,and printinga teletypewriter character at the end of each interruption,each printed character corresponding to the duration of eachinterruption.

3. The combination of a plurality of stations between which signals maybe transmitted each station including a key for producing a plurality ofcoded pulses of current and a selector which may respond to apredetermined coded pulse, means for observing the lengths of thevarious interruptions of any key While it is in service, said meansincluding a teletypewriter which is started at the beginning of eachinterruption and prints a teletypewriter character at the end of eachinterruption, the characters printed corresponding to the lengths of theinterruptions.

JAMES T. NEISWINTER.

